Reading a hardware register in Embedded C

Introduction

Reading a hardware register lets your program check the status or data from a device connected to your system.

When you want to know if a button is pressed on a device.

When you need to read sensor data like temperature or pressure.

When checking if a device is ready to send or receive data.

When monitoring error or status flags from hardware.

When controlling hardware by reading its current state.

Syntax

Embedded C

volatile uint32_t *REG = (volatile uint32_t *)0x40021000;
uint32_t value = *REG;

Use volatile to tell the compiler the value can change anytime outside the program.

The address (like 0x40021000) is the hardware register location.

Examples

Read the status register at address 0x40021004.

Embedded C

volatile uint32_t *STATUS_REG = (volatile uint32_t *)0x40021004;
uint32_t status = *STATUS_REG;

Read a 16-bit data register at address 0x40021008.

Embedded C

volatile uint16_t *DATA_REG = (volatile uint16_t *)0x40021008;
uint16_t data = *DATA_REG;

Read an 8-bit control register at address 0x4002100C.

Embedded C

volatile uint8_t *CONTROL_REG = (volatile uint8_t *)0x4002100C;
uint8_t control = *CONTROL_REG;

Sample Program

This program simulates reading a hardware register by using a variable. It reads the value and prints it in hex format.

Embedded C

#include <stdint.h>
#include <stdio.h>

// Simulate hardware register at this address
volatile uint32_t simulated_register = 0xABCD1234;

int main() {
    // Pointer to the simulated hardware register
    volatile uint32_t *REG = &simulated_register;

    // Read the value from the hardware register
    uint32_t value = *REG;

    // Print the value in hexadecimal
    printf("Register value: 0x%08X\n", value);

    return 0;
}

Important Notes

Always use volatile when working with hardware registers to prevent unwanted compiler optimizations.

Hardware register addresses are fixed and given by the device datasheet.

Reading a register may have side effects depending on the hardware, so read carefully.

Summary

Reading a hardware register means accessing a special memory address to get device data.

Use a pointer with volatile to read the register safely.

The register address comes from the hardware documentation.